The present disclosure relates to an installing structure for an electric variable valve timing mechanism, which is actuated by an electric motor attached to a chain cover.
In recent years, a number of internal combustion engines, which are drive sources mounted in vehicles such as automobiles, have been equipped with variable valve timing apparatuses for varying the opening-closing timing of engine valves (so-called, valve timing) of intake valves or exhaust valves. Japanese Laid-Open Patent Publication No. 2009-293574 proposes the use of an electric type variable valve timing apparatuses.
An electric variable valve timing apparatus, for example, has the configuration described below. This variable valve timing apparatus includes a sprocket unit fixed to one end of the camshaft of the internal combustion engine. The sprocket unit includes a first rotor fixed to one end of the camshaft, a second rotor surrounding the circumference of the first rotor, and a sprocket, which is integrally formed with the outer periphery of the second rotor. A timing chain is looped over the sprocket. The sprocket unit also includes a varying mechanism, which is located between the first rotor and the second rotor to couple the first rotor and the second rotor while allowing the rotors to rotate relative to each other. The variable valve timing apparatus further includes an electric motor for actuating the varying mechanism. The electric motor is fixed to the chain cover with bolts and coupled to the varying mechanism.
In the variable valve timing apparatus, the varying mechanism is actuated through control of the electric motor to change the relative rotational angle between the first rotor and the second rotor. This changes the relative rotational angle between the camshaft, which is fixed to the first rotor, and the crankshaft, which is coupled to the second rotor by the timing chain and the sprocket. Accordingly, the valve timing is varied.
In the above described variable valve timing apparatus, the sprocket unit is arranged in the space that is covered by the chain cover, that is, the space defined by the chain cover and the engine body (the cylinder head and the cylinder block). Thus, for example, at repair of the variable valve timing apparatus, removing operation or attaching operation of the sprocket unit particularly with the engine mounted in the vehicle needs to be performed in the narrow space covered by the chain cover. Therefore, the worker may inadvertently drop the sprocket unit into the space.